Adsorption of organic acids from amniotic fluid and urine onto silica gel before analysis by gas chromatography and combined gas chromatography/mass spectrometry.

We describe a method for adsorbing organic acids from amniotic fluid and urine specimens onto a column of silica gel before analysis by gas chromatography and by combined gas chromatography/mass spectrometry. Analytical recoveries of individual organic acids by our adsorption method compare favorably with those obtained by a more laborious manual extraction with ethyl acetate. Results for specimens of amniotic fluid and urine show that our method gives better recoveries of most of the organic acids. Furthermore, because citric acid is also extracted in our method without extracting significant amounts of sulfate or phosphate, the method is a suitable alternative to methods involving the use of DEAE-Sephadex for concentrating these acids.